Obtaining materials that are perfectly adaptable in their usage has been a constant challenge for science and technology in recent years. The growing demand for materials that have an appropriate balance of important and specific properties, added to the ecological restrictions of utilization, has produced great efforts from scientists in the search for innovative solutions to these challenges.
The science of polymers has made a decisive contribution to this process. Due to intensive research and the use of sophisticated processes of polymerization, new products have been obtained, with a combination of properties that until now were not found in traditionally known materials. The emphasis with respect to the environment has guided this research and generated processes and products that are increasingly ecologically appropriate.
Among the wide variety of polymers, the elastomers are the best known. Due to their large capacity to deform elastically when submitted to tension and then return spontaneously to their original form when the tension ceases, elastomers can be employed to obtain many important products when correctly used in the form of vulcanized compounds. Among these products are mainly tires, in all their complexity, including their constituents such as the tread, sidewalls etc, as well as mats, straps and a wide range of technical products.
These rubber or elastomeric products, in determinate applications, need to present a series of properties, which cannot always be combined simultaneously. In the case of tires for automobiles, the following properties are required; elasticity, low abrasion wear, good adhesion on different surfaces, and wet skid resistance, in low and high temperatures. Performance improvement in one of these properties normally results in a decrease in the performance in one of the others. This is equally undesirable and most of the time it becomes impossible to optimize all the properties.
A number of solutions have been used by tire manufacturers, with the objective of combining and improving the different properties of their products. This has essentially consisted in the combined use of different elastomers in the utilization of different reinforcement loads, which interact physically and chemically with the elastomers, and in the use of compatible additives in the preparation of the vulcanized rubber compounds.
For example, tires manufactured with elastomers of the type SBR (copolymers 1,3-butadiene-styrene), including those produced in a cold emulsion (E-SBR) and those produced in a solution (S-SBR), with a chemical content of combined styrene of approximately 23%, present a high wet skid resistance, and also a high rolling resistance. The tires that are manufactured with conventional elastomers such as the 1,4-Cis BR (polybutadiene High Cis), NR (Natural Rubber) and IR (Polyisoprene), present low rolling resistance and low wet skid resistance (P. L. A. Coutinho, C. H. Lira, L. F. Nicolini, A Ferreira; Elastomers for the “Green Tire”, 1st Chemical and Petrochemical Industry Congress of Mercosur, Buenos Aires, Argentina, 1998). The appropriate combination of these different elastomers, in vulcanized compounds, allows the production of tires with an improved balance of properties.
Moreover, the use of compatible additives, utilized in the preparation of vulcanized compounds, or even the employment of modified elastomers in the polymeric structure, including the incorporation of specific functional groups, increases the miscibility between the different elastomers, as well as their interaction with the reinforcement loads, which markedly improves the resulting properties of the tire.
As has been described in other researches, an increase in the chemical content of the 1,2-vinylic units, in the polydienic sections of the elastomers of type S-SBR, results in an increase of its glass transition temperature Tg), which provides an improvement in the skid resistance properties of the vulcanized compounds for tires. (C. H. Lira, L. F. Nicolini, G. Weinberg, N. M. T. Pires, Coutinho—Elastomers For High Performance Tires—Presented at a Meeting of the Rubber Division, American Chemical Society, Cleveland, Paper No 112, 2001).
Moreover, it was demonstrated that a higher chemical content of these units assists the solubility of the elastomers of type S-SBR in other elastomers, such as 1,4 Cis-BR and NR (R. H. Schuster, H. M. Issel and V. Peterseim—Selective Interactions in Elastomers; A Base for Compatibility and Polymer-Filler Interactions; Rubber Chem. Technol., 69, 5, 1996).
Therefore, any structural modification that can be incorporated into the different elastomers that assists the miscibility between them, besides providing an improved compatibility with the different reinforcement fillers employed in the vulcanized elastomeric compounds, also improves the resulting properties of the tires.
There is a special interest in the tread, the part of the tire where the main mechanical forces are concentrated and where the properties with respect to safety, such as wet/icy skid resistance, are demanded.
The elastomeric compounds used in the production of tires, especially in the tread, are normally composed of copolymers, formed by a conjugated diene and a monomer with an aromatic vinyl structure.
Elastomers of type S-SBR are mainly used. These copolymers present a predominantly random distribution of their constituent mers along their polymeric chains and can also present sections with blocked distribution, or a mixture of random and blocked distribution. They are decisive in the obtainment of the final properties of the tire. The following material deals with the current state of the art and is incorporated in its entirety as a reference.
As has been previously stated, the state of the art with respect to tires, especially the tread, requires a level of development that allows the employment of new materials, or rather polymers, which provide tires (and the tread) with a high performance, in view of given vehicle and tire performance conditions.
In the documentation of patent EP 0929582 (U.S. Pat. No. 6,013,718) and EP 1110998 (U.S. Pat. No. 6,667,362 B2), there is a description of the preparation and use of polydienes and copolymers resulting in the copolymerization between the conjugated dienes and a monomer with an aromatic vinyl structure (e.g.: S-SBR), which contains functional groups of siloxane and silanol in the end section of the polymeric chains. These groups interact with the silica used in the vulcanized compounds, improving its properties. The patents display the comparative results obtained from the employment of these elastomers in several vulcanized elastomeric compounds.
The patent GB 2368069 describes the process of the preparation of the functionalized polymers in both the extremities of the polymeric chains. Its structure is essentially that of a triblock, where the intermediary section can be a polydiene or a copolymer, resulting from the copolymerization between the conjugated diene and a monomer with an aromatic vinyl structure (e.g.: S-SBR), where the end sections are preferentially polydialkylsiloxanes.
The patent EP 0849 333 B2 describes the use of siloxanes substituted in the preparation of the polydienes or copolymers, resulting from the copolymerization between the conjugated dienes and a monomer with an aromatic vinyl structure. The use of these functionalized polymers in vulcanized elastomeric compounds and their observed properties are also presented.
In view of the abovementioned state of the art developments, this invention provides a product and a process of preparation of a new family of elastomers of type S-SBR, designed principally for the production of high performance tires. The production of these elastomers uses advanced processes of polymerization, allowing larger control over the macrostructure and microstructure of the polymer.
The elastomeric product thus produced allows for the production of tires with highly desirable performance specifications, particularly with respect to the tread.